Robert E. Taylor

The distribution of membrane current in nerve with longitudinal linearly increasing applied current

The distribution of membrane current in three models of nerve, when a longitudinal, linearly increasing current is applied, is derived. For the simple core conductor model it is shown that, if the region over which such a current is applied is large compared to the space constant of the model, the membrane current in the mid-portion of the region is a constant, independent of the distance, the time following the application of the current, and the impedance of the membrane. The effect of nonlinear membrane electrical properties is discussed. It is further shown that these conclusions apply equally to the case in which the simple model is surrounded by another concentric sheath (the double cable model). In this case the impedance of the sheath does not influence the membrane current in the mid-polar region. Finally, it is shown that the form of the solution for the saltatory model, for this type of applied current, is identical with that for the simple model.

Characterization of porous material and a sound suppression system using a shock tube

This work describes the design and construction of an experimental apparatus for testing shock waves and a sound suppression system for student learning. The shock tube will be used to characterize both porous media and the suppression system response to a non-linear shockwave. The effects of a plane shock wave will be used to determine acoustic properties, such as transmission, reflection, and absorption coefficients, of rigid frame porous materials. The suppression system is comprised of 20 conical chambers that cause a loss of energy in the shock wave by the expansion and acceleration of the flow. The sound pressure level from the shock is in excess of 140 dB re 20 μPa. Material properties and the performance of the designed suppression system will be presented.

Numerical investigation on transmission loss of sound above sea surface

Determination of the transmission loss of sound travelling over the ocean with various sea states involves a number of variables. One method to approximate the random roughness of the surface is to use the variance spectrum model as proposed by Pierson and Moskowitz. A numerical solution of the wave equation is presented for a small elevation angle over the sea surface at different sea states. This new model has the capability to include both the thermal gradient and wind profile above the sea. The solutions are derived with an implementation of the Crank-Nicolson Parabolic Equation, and the ocean wave roughness profile is introduced into the numerical model by the Generalized Terrain Parabolic Equation method. These results are used to investigate the effect of the sea roughness on the sound transmission loss for different sea states.

Resonance frequencies of a spherical aluminum shell subject to static internal pressure

Measurements of the vibrational response of a spherical aluminum shell subject to changes in the interior pressure clearly demonstrate that resonance frequencies shift higher as the pressure is increased. The frequency shift appears to be smaller for longitudinal modes than for bending wave modes. The magnitude of frequency shift is comparable to analytical predictions made for thin cylindrical shells. Changes in the amplitudes of resonance peaks are also observed. A possible application of this result is a method for noninvasively monitoring pressure changes inside sealed containers, including intracranial pressure in humans.

Acoustical testing and treatment of elementary schools, St. Louis International Airport environs

Since 1986 a school acoustical treatment has been funded by Airport Community Programs Office (ACPO), St. Louis International Airport. The program has included selection of candidate schools, inside–outside noise tests, providing acoustical treatment recommendations, construction, and the postconstruction testing of elementary schools within the environs of St. Louis International Airport (Lambert Field). This paper summarizes the results of the first eight schools. Three schools remain in the program and await funding for the construction phase. Although the instrumentation and the type of noise tests has varied somewhat over the years, the primary goal was to reduce the classroom noise to below the Leq 45 level per FAA guidelines. SEL and 1/3‐oct band data from overflights were also evaluated in some schools. The improvement in classroom Leq varied from 8 to 15.7 dBA in the classrooms tested. The acoustical improvements specified included acoustic windows and doors, interior acoustical treatment, new ro...